| 21. |
- Liu, Lijun, et al.
(författare)
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Simulating two-phase flow and geomechanical deformation in fractured karst reservoirs based on a coupled hydro-mechanical model
- 2021
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Ingår i: International Journal of Rock Mechanics And Mining Sciences. - : Elsevier BV. - 1365-1609 .- 1873-4545. ; 137
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Tidskriftsartikel (refereegranskat)abstract
- Two-phase flow in fractured and karstified porous media subject to coupled hydro-mechanical conditions is an important issue for oil recovery in carbonate reservoirs. However, due to the co-existence of porous media flow, fracture flow and free flow, as well as their couplings with geomechanical deformation, modeling the behavior of fractured karst systems remains challenging. In this work, a novel coupled hydro-mechanical model for simulating the complex behavior of fractured and karstified porous media is developed. Two-phase Darcy's equation is used to describe fluid flow in both matrix and fractures, while the free flow in cavities is considered based on an assumption of phase instantaneous gravity segregation. A modified Barton-Bandis's constitutive model is used to mimic the nonlinear fracture deformation. The cavity deformation is solved based on the fluid pressure on the cavity boundaries. A mixed finite volume-finite element method and a fixed-stress iterative splitting method are adopted to numerically solve the coupled system of equations. The model is then applied to a series of 2D and 3D problems to unravel the impacts of fractures and cavities on two-phase flow and geomechanical deformation in fractured karst systems. The results indicate that cavities hinder water breakthrough due to storage effects, while water may quickly migrate through highly conductive fractures. Cavities tend to dominate the flow and mechanical processes even though fractures are present as well. Significant stress concentration is observed around cavities. Furthermore, the results of 3D cases imply that phase gravity segregation in cavities leads to lower water saturation in the area above cavities and delays water breakthrough.
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| 22. |
- Liu, Qinghua, et al.
(författare)
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Advanced electrolyte-free fuel cells based on functional nanocomposites of a single porous component : analysis, modeling and validation
- 2012
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 2:21, s. 8036-8040
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Tidskriftsartikel (refereegranskat)abstract
- Recently, a fuel cell device constructed with only one layer composited of ceria-based nanocomposites (typically, lithium nickel oxide and gadolinium doped ceria (LiNiO2-GDC) composite materials), called an electrolyte-free fuel cell (EFFC), was realized for energy conversion by Zhu et al. The maxium power density of this single-component fuel cell is 450 mW cm(-2) at 550 degrees C when using hydrogen fuel. In this study, a model was developed to evaluate the performance of an EFFC. The kinetics of anodic and cathodic reactions were modeled based on electrochemical impedance spectroscopy (EIS) measurements. The results show that both of the anodic and cathodic reactions are kinetically fast processes at 500 degrees C. Safety issues of an EFFC using oxidant and fuels at the same time without a gas-tight separator were analyzed under open circuit and normal operation states, respectively. The reaction depth of anodic and cathodic processes dominated the competition between surface electrochemical and gas-phase reactions which were effected by the catalytic activity and porosity of the materials. The voltage and power output of an EFFC were calculated based on the model and compared with the experimental results.
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| 23. |
- Liu, Qinghua, et al.
(författare)
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Theoretical description of superionic conductivities in samaria doped ceria based nanocomposites
- 2010
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 97:18, s. 183115-
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Tidskriftsartikel (refereegranskat)abstract
- Superionic conductivity becomes true based on recent developments on ceria-based nanocomposites as electrolytes with application for low temperature (300-600 degrees C) solid oxide fuel cells. We theoretically describe the superionic conductivity phenomena in samaria doped ceria nanocomposites. An improved effective-medium model was used to determine the ionic conductivity of the materials focusing on a core-shell structure of the as-prepared samaria doped ceria based composite particles. This work reveals the enhancement of ionic conductivity by interface proton and oxygen ion transportation in the composites, which agrees well with the experimental results.
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| 24. |
- Liu, Zhouying, et al.
(författare)
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Exploring askers' switching from free to paid social Q&A services : A perspective on the push-pull-mooring framework
- 2021
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Ingår i: Information Processing & Management. - : Elsevier BV. - 0306-4573 .- 1873-5371. ; 58:1
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of this study is to explore the factors that prompt askers to switch from free to paid social question-and-answer (SQA) services. Prior studies have investigated users' motivations and participation in free and paid SQA services; however, little attention has been paid to askers' switching behavior. We empirically analyzed the content of qualitative interviews from 64 askers on a well-known SQA platform in China. Based on the push-pull-mooring framework, we identified and classified factors that influenced askers' to switch from free to paid Q&A services, using the critical incident technique, after which we calculated the entropy weights of the 16 subcategories before and after the switch, using the entropy weight method. The findings suggest that askers' switching behavior was influenced by push factors (i.e., dissatisfaction with the free SQA service), pull factors (i.e., satisfaction with the paid SQA service), and mooring factors (i.e., social factors, personal factors, situational factors). Moreover, the findings show that the effects of these factors vary significantly before and after a switch. Dissatisfaction with the quality of information from the free SQA service would influence users before a switch, whereas satisfaction with the quality of information from the paid SQA service would influence them after a switch. In terms of mooring factors, the effects of social and personal factors on askers' switching behavior, especially subjective norms and cognitive lock-in, turn out to be less significant after a switch, whereas the effect of trust is more significant. Besides, the effects of situational factors are more or less the same before and after a switch. To the best of our knowledge, this paper is one of the first attempts to explore factors that affect askers' switching behavior and to shed light on the managerial strategies of paid SQA services.
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| 25. |
- Qin, Haiying, et al.
(författare)
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Direct biofuel low-temperature solid oxide fuel cells
- 2011
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Ingår i: ENERGY & ENVIRONMENTAL SCIENCE. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 4:4, s. 1273-1276
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Tidskriftsartikel (refereegranskat)abstract
- A low-temperature solid oxide fuel cell system was developed to use bioethanol and glycerol as fuels directly. This system achieved a maximum power density of 215 mW cm(-2) by using glycerol at 580 degrees C and produced a great impact on sustainable energy and the environment.
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| 26. |
- Raza, Rizwan, 1980-, et al.
(författare)
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Advanced Multi-Fuelled Solid Oxide Fuel Cells (ASOFCs) Using Functional Nanocomposites for Polygeneration
- 2011
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Ingår i: Advanced Energy Materials. - Germany : Wiley-VCH Verlagsgesellschaft. - 1614-6832 .- 1614-6840. ; 1:6, s. 1225-1233
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Tidskriftsartikel (refereegranskat)abstract
- An advanced multifuelled solid oxide fuel cell (ASOFC) with a functional nanocomposite was developed and tested for use in a polygeneration system. Several different types of fuel, for example, gaseous (hydrogen and biogas) and liquid fuels (bio-ethanol and bio-methanol), were used in the experiments. Maximum power densities of 1000, 300, 600, 550 mW cm−2 were achieved using hydrogen, bio-gas, bio-methanol, and bio-ethanol, respectively, in the ASOFC. Electrical and total efficiencies of 54% and 80% were achieved using the single cell with hydrogen fuel. These results show that the use of a multi-fuelled system for polygeneration is a promising means of generating sustainable power.
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| 27. |
- Raza, Rizwan, et al.
(författare)
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La 0.3Sr 0.2Mn 0.1Zn 0.4 oxide-Sm 0.2Ce 0.8O 1.9 (LSMZ-SDC) nanocomposite cathode for low temperature SOFCs
- 2012
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Ingår i: Journal of Nanoscience and Nanotechnology. - : American Scientific Publishers. - 1533-4880 .- 1533-4899. ; 12:6, s. 4994-4997
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Tidskriftsartikel (refereegranskat)abstract
- Nanocomposite based cathode materials compatible for low temperature solid oxide fuel cells (LTSOFCs) are being developed. In pursuit of compatible cathode, this research aims to synthesis and investigation nanocomposite La 0.3Sr 0.2Mn 0.1Zn 0.4 oxide-Sm 0.2Ce 0.8O1.9 (LSMZ-SDC) based system. The material was synthesized through wet chemical method and investigated for oxideceria composite based electrolyte LTSOFCs. Electrical property was studied by AC electrochemical impedance spectroscopy (EIS). The microstructure, thermal properties, and elemental analysis of the samples were characterized by TGA/DSC, XRD, SEM, respectively. The AC conductivity of cathode was obtained for 2.4 Scm ?1 at 550 °C in air. This cathode is compatible with ceria-based composite electrolytes and has improved the stability of the material in SOFC cathode environment.
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| 28. |
- Raza, Rizwan, et al.
(författare)
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ZnO/NiO nanocomposite electrodes for low-temperature solid oxide fuel cells
- 2011
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Ingår i: Electrochemistry communications. - : Elsevier BV. - 1388-2481 .- 1873-1902. ; 13:9, s. 917-920
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Tidskriftsartikel (refereegranskat)abstract
- ZnO/NiO nanocomposite electrodes have successfully been developed using a cost-effective method, and for the first time used in LT-SOFCs at 300-600 degrees C. They exhibit high conductivity and a dual catalytic functionality in both the cathode and the anode for the electrochemical reduction of O(2) and oxidation of H(2), respectively. An excellent fuel cell performance, e.g. a maximum power density of 1107 W cm(-2), has been shown for a symmetrical fuel cell that contained ZnO/NiO nanocomposite electrodes at 500 degrees C. To our knowledge, to date this is by far the highest power density achieved at this temperature.
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| 29. |
- Ruan, Ting, et al.
(författare)
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Presence and partitioning behavior of polyfluorinated iodine alkanes in environmental matrices around a fluorochemical manufacturing plant : another possible source for perfluorinated carboxylic acids?
- 2010
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 44:15, s. 5755-5761
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Tidskriftsartikel (refereegranskat)abstract
- The indistinct origins of some ubiquitous perfluorinated alkyl acids have attracted great attention in recent decades. In this present work, even-chained polyfluorinated iodides (PFIs), a group of volatile perfluorinated compounds (PFCs), including four perfluorinated iodine alkanes (FIAs) and three polyfluorinated telomer iodides (FTIs) were confirmed to be present in the environment. A wide concentration range was found for FIAs at 1.41 to 3.08x104 pg/L, and for FTIs at 1.39 to 1.32x103 pg/L in the ambient air collected around a fluorochemical manufacturing plant in Shandong province, northern China. Whereas for surface soils, most of these PFIs were below detection limits and only small amounts of analytes with higher carbon chain (such as perfluorododecyl iodide and 1H,1H,2H,2H-perfluorodecyl iodide, 16.6-499 pg/g) could be sporadically detected. The presence of the PFIs in different environmental matrices in the investigated area and calculated vapor pressures (0.095-20.4 Torr) verify that they can be considered as volatile organic chemicals and easily be released into the atmosphere. Together with reported degradation ability and long-range transport potential, the identification of these PFIs indicates that unintentional release during the telomer reaction process might also be another route for the formation and distribution of certain polyfluorinated alcohols, aldehydes, and carboxylic acid derivatives under oxidative conditions in the environment.
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| 30. |
- Sun, Yongfu, et al.
(författare)
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Fabrication of flexible and freestanding zinc chalcogenide single layers
- 2012
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 3, s. 1057-
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Tidskriftsartikel (refereegranskat)abstract
- Inorganic graphene analogues (IGAs) are a conceptually new class of materials with attractive applications in next-generation flexible and transparent nanodevices. However, their species are only limited to layered compounds, and the difficulty in extension to non-layered compounds hampers their widespread applicability. Here we report the fabrication of large-area freestanding single layers of non-layered ZnSe with four-atomic thickness, using a strategy involving a lamellar hybrid intermediate. Their surface distortion, revealed by means of synchrotron radiation X-ray absorption fine structure spectroscopy, is shown to give rise to a unique electronic structure and an excellent structural stability, thus determining an enhanced solar water splitting efficiency and photostability. The ZnSe single layers exhibit a photocurrent density of 2.14 mA cm(-2) at 0.72 V versus Ag/AgCl under 300 W Xe lamp irradiation, 195 times higher than that of bulk counterpart. This work opens the door for extending atomically thick IGAs to non-layered compounds and holds promise for a wealth of innovative applications.
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